The present invention relates to the formation of a metal coated thin wall plastic printing cylinder for flexographic and rotogravure printing.
There have been many attempts to produce plastic based, metal coated printing plates or rolls since the advantages of such products are readily apparent. That is, the resulting printing plates or rolls would be relatively lightweight which would facilitate handling, transfer and storage. There are a number of patents dealing with metal coated plastic printing plates (see for example U.S. Pat. Nos. 3,558,290; 3,483,074; 3,351,009; and others).
Generally, copper is the preferred metal for the external surface of the printing plate or roll to receive the printing image. The coating of copper onto a base metal (e.g., iron or steel) is relatively straightforward but the coating of copper onto a non-conductive substrate can be difficult. U.S. Pat. No. 3,483,074 discloses a printing plate which is made of a filled polyethylene coated with silver and then copper. However, silver is quite expensive so this method is not commercially feasible. In addition, it has been found that the mode of application of copper is often important in determining the ultimate utility of the printing base and particularly for use in rotogravure printing cylinders.
Rotogravure printing cylinders contain an etched metal (generally copper) surface which is the desired printed image. One of the difficulties with metal coated plastic based printing cylinders has been the ability to plate copper onto the plastic cylinders. While such a coating has occasionally been done, it has been found that in use, the copper layer tends to separate and/or blister and ultimately separate from the plastic cylinder. Rotogravure printing is known to be a high quality process used for the production of wallpaper, packaging materials, floor covering, tag and label and other, more or less continuously printed patterns which can be run in relatively long runs. The rotogravure printing cylinder prints on a complete 360 degree circumference. Maintaining a stable metal coating on a roll or cylinder under rotogravure printing conditions is more difficult than maintaining it stable on a plate which is used in a flat condition during printing. In addition, rotogravure printing requires the use of the roll at substantial pressures and high surface speed. These conditions of use tend to aggravate the separation problems found with metal coated plastic printing rolls. The art, thus, has not sufficiently developed to produce a reliable thin wall plastic based, metal coated printing plate suitable for use in rotogravure and/or flexographic printing operations.
As noted, another advantage of a lightweight plastic based rotogravure printing roll is its ability to be handled and stored as compared to conventional copper plated, steel printing cylinders. It would be particularly useful to have a plastic-based printing cylinder that could be replaced by a similar plastic-based printing cylinder having the same or a different printing image without having to take apart the printing press and particularly without having to take apart at least one of the journal portions of the printing press since, in that fashion, alignment of the new metal coated plastic-based cylinder could be made substantially quicker. In the installation of a conventional copper-coated steel rotogravure cylinder today, alignment can take several hours.
Recent patents on metal coated, plastic-based intaglio printing cylinders include U.S. Pat. Nos. 4,197,798 and 4,301,727. In each of these patents the plastic cylinder base is rather massive and generally resembles a conventional printing cylinder in which the steel or iron has been replaced by a fiber-filled plastic and onto which an etchable copper surface is directly electroplated. However, this construction requires a rather precise plastic cylinder as well as a relatively complicated electroplating procedure to plate the copper onto the massive plastic base. In addition, these cylinders do not have several of the desired features discussed above and suffer from the problems relating to copper/plastic adherence noted above.
It is therefore an object of the present invention to provide means for alleviating the problems of the prior art.
It is a further object of the present invention to provide metal coated, thin wall plastic cylinders for use in flexographic and rotographic printing and methods of making same.
It is another object of the present invention to provide thin wall metal coated plastic printing cylinders for flexographic and rotographic printing which can be quickly and easily replaced and aligned in the printing machinery.